The present invention relates to a handgrip with a built-in heater and intended for use on a motorcycle or the like. More particularly, the invention relates to a handgrip with a built-in flexible printed circuit heater circuit (hereafter simply referred to as an FPC heater), which is a planar heater.
Conventionally, it has been known to incorporate a planar heater into the handgrips of a handlebar of a motorcycle to heat the handgrips as needed.
FIGS. 12 and 13 are cross-sectional views illustrating an example of a handgrip with a built-in heater of this type. (See Japanese Utility Model Application Laid-Open No. 60996/1993). Reference numeral 1 denotes a handgrip body which can be integrally fitted over and secured to a handle pipe 2 as the handle pipe 2 is inserted into the handgrip body 1. The handgrip body 1 has a structure in which a cladding layer 5 made of soft rubber is molded integrally over the outer periphery of a synthetic resin inner piece 3 having a semicircular cross section as well as appropriate rigidity, and around which an FPC heater 4 is wound. A rubber layer 6 for making pressure contact with the pipe is provided on the inner peripheral surface of the inner piece 3, thereby making it possible to positively hold and fix the handgrip body 1 onto the handle pipe 2.
With the handgrip shown in FIGS. 12 and 13, however, the FPC heater 4 extends around only about half the circumference of the handgrip 1 body, so that only about half the area of the handgrip body 1 is directly warmed.
To overcome this problem, as shown in FIG. 14, a handgrip with a built-in heater has been proposed in which an FPC heater 4 is wound around the outer peripheral surface of a substantially hollow cylindrical inner piece 3 having a peripheral portion 3a which is slotted, and the cladding rubber layer 5 is molded thereon. Also, though not shown, a handgrip with a built-in heater in which the inner piece 3 is formed in a hollow cylindrical shape has been proposed. Since the FPC heater 4 extends substantially over the entire periphery of the handgrip body, the rider's hand gripping the handgrip can be warmed efficiently.
In FIG. 14, reference numeral 7 denotes grooves which extend circumferentially and axially on the inner peripheral surface of the inner piece 3. The rubber layer 6 for making pressure contact with the pipe is filled in these grooves 7.
With the above-described conventional handgrip heater shown in FIG. 14, the grooves 7 filled by the rubber layer 6 for making pressure contact with the pipe need to be formed on the inner peripheral surface of the inner piece 3. However, since the inner piece 3 is of a hollow cylindrical or a substantially hollow cylindrical configuration, it is very difficult to form the grooves 7. The manufacture of a handgrip with a built-in heater has been troublesome for this reason.